The present invention relates to a rotor of a centrifugal separator which is widely used in medical, pharmaceutical, and genetic engineering and other various fields.
Especially, the present invention relates to a rotor of a centrifugal separator which is preferably used to perform high-speed centrifugal operation of a microplate casing or a microtube assembly.
The microplate casing is a boxlike sample container whose size is approximately 130 mm in vertical width, approximately 90 mm in lateral width, and 10˜50 mm in height. A plurality of sample storing recesses are formed on an upper surface of the microplate casing. The sample storing recesses are arranged in a predetermined matrix pattern consisting of a plurality of rows and lines. Each sample storing recess has a capacity and a depth sufficient for storing a liquid sample, such as blood components and culture solution, to be centrifuged for test or inspection.
The microtube assembly is similar to the microplate casing in size and configuration. The microtube assembly has an inside space for accommodating a plurality of plastic microtubes.
The microplate casing is generally made of plastic material such as polystyrene or polypropylene and is formed by molding. The microplate casing is disposable.
For example, the unexamined Japanese patent publication No. 50-156989, Japanese Utility Model No. 57-934, unexamined Japanese patent publication No. 9-155235, and unexamined Japanese patent publication No. 9-155236 disclose conventional rotors for the microplate casings.
FIG. 5 shows a representative conventional rotor. The conventional rotor shown in FIG. 5 chiefly consists of a rotor body 21, two buckets 23, and an adapter 24. The rotor body 21 is rotatable about a drive shaft 21 a when driven by a drive motor or any other actuator (not shown). The rotor body 21 has an H-shaped configuration with two cutout portions at the longitudinal ends thereof. In other words, each longitudinal end of the rotor body 21 is bifurcated so as to serve as arms for holding the bucket 23. Each bucket 23 is swingable about its shafts 23a. Both shafts 23a are supported by the bifurcated arms of rotor body 21. Two buckets 23 are positioned symmetrically with respect to the drive shaft 21a. When the rotor body 21 rotates for centrifugal operation, a centrifugal force acts on each bucket 23. The buckets 23 swing radially outward about their shafts 23a due to the centrifugal force. The buckets 23 face each other and are positioned in an opposed relationship during the centrifugal operation. The microplate casing is fixed in the bucket 23 via the adapter 24. Thus, the liquid sample stored in the microplate casing is subjected to the centrifugal force (i.e., a centrifugal acceleration). According to the arrangement of this conventional rotor, the maximum rotational speed reaches 2,000 to 6,000 rpm. The maximum centrifugal acceleration reaches 600 to 5,000Xg.
The recent representative application field of the centrifugal rotors is a genetic engineering. Highly advanced centrifugal rotors are the key for improving the efficiency of DNA and RNA related researches. In the process of DNA sequencing in this field, the centrifugal operation of DNA samples has an important role. Especially, in an ethanol sedimentary processing, an appropriate amount of ethanol is added to DNA containing solution and then the centrifugal operation is performed to collect or recover DNA. Conventionally, a plastic microtube (a sort of test tube) of 0.2 ml to 2 ml is used. The angle rotor or swing rotor, applicable to this plastic microtube, is rotated for the centrifugal operation at 12,000 rpm (equivalent to 10,000Xg) for 10 minutes. A microplate rotor is also used to perform the centrifugal operation at 6,000 rpm (equivalent to 5,000Xg) for 30 minutes.
According to the former centrifugal operation, an operator is required to handle each one of microtubes. This complicates the centrifugal operation and worsens the efficiency of centrifugal operation. The number of microtubes processible at the same centrifugal operation was limited to approximately 48 due to structural restrictions of the centrifugal separator.
According to the latter centrifugal operation, the microplate can process numerous samples at a time. However, the reachable centrifugal acceleration is dissatisfactory and the separation time is longer than 30 minutes. This worsens the efficiency of centrifugal operation.
The rotor disclosed in the unexamined Japanese patent publication No. 9-155236 obtains a high centrifugal force under the condition that the microplate casing is held in a perpendicular condition. However, after finishing the centrifugal operation, the separated sample is rotated from the upright position (90°) to the lying position (0°). This undesirably promotes remixing of the separated sample and the solution.
The centrifugal separators are widely used to perform health-related inspections, DNA and RNA related researches, tissue culture experiments or the like. The key for promptly accomplishing these inspections, researches, and experiments is to improve the efficiency of centrifugal operation required in an intermediate process of the inspection or the experiment,
The efficiency of centrifugal operation can be improved by increasing the centrifugal acceleration given to the sample (i.e., by increasing the rotational speed of the centrifugal rotor). The efficiency of centrifugal operation can be also improved by increasing the number of simultaneously processible specimens.
The microplate casing has excellent capacity for processing as many as 96 specimens at a time. However, the conventional microplate swing rotors cannot increase the maximum rotational speeds due to their structural restrictions. Furthermore, the swing rotors have larger diameters. This inevitably induces the windage loss during the centrifugal operations. Thus, the swing rotors cannot increase the rotational speed as intended.
Moreover, according to the centrifugal rotor which holds the microplate in a perpendicular position during the centrifugal operation, the separated sample is turned 90° from the rotational condition to the stopped condition. Some samples will mix with the solution again. This is not appropriate.
A microplate rotor disclosed in the unexamined Japanese patent publication No. 50-156989 has an inclined arrangement in a stationary condition. However, according to this conventional microplate rotor, a rotational shaft must bear the centrifugal forces acting on both a basket and the microplate during rotation of the rotor. This kind of conventional microplate rotor cannot be used for high-speed centrifugal operation.